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PEOPLE@HES-SO – Annuaire et Répertoire des compétences
PEOPLE@HES-SO – Annuaire et Répertoire des compétences

PEOPLE@HES-SO
Annuaire et Répertoire des compétences

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Pavanello Davide

Pavanello Davide

Professeur-e HES Associé-e

Compétences principales

Réseaux électriques

Electric power systems

Protection des réseaux électriques

Production répartie

Power systems protection

Foudre

Lightning discharge

  • Contact

  • Enseignement

  • Publications

  • Conférences

Contrat principal

Professeur-e HES Associé-e

Téléphone: +41 58 606 87 61

Bureau: ENP.23.N417

HES-SO Valais-Wallis - Haute Ecole d'Ingénierie
Rue de l'Industrie 23, 1950 Sion, CH
HEI - VS
Domaine
Technique et IT
Filière principale
Energie et techniques environnementales
Institut
Institut Energie et environnement
BSc HES-SO en Energie et techniques environnementales - HES-SO Valais-Wallis - Haute Ecole d'Ingénierie
  • Réseaux électriques
  • Électrotechnique

2019

A study of a large bipolar lightning event observed at the Säntis tower
Article scientifique ArODES

Mohammad Azadifar, Marcos Rubinstein, Farhad Rachidi, Vladimir A. Rakov, Gerhard Diendorfer, Wolfgang Schulz, Davide Pavanello

IEEE Transactions on Electromagnetic Compatibility,  2019, vol. 61, no. 3, pp. 796-806

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Résumé:

An unusual negative lightning flash was recorded at the Säntis Tower on June 15, 2012. The flash did not contain an initial continuous current typical of upward negative lightning, which is the most common type of event at the Säntis Tower. The flash contained four strokes, the last three of which were normal while the current associated with the first stroke resembled a Gaussian pulse with an unusually high peak value of 102.3 kA, a long risetime of 28.4 μs, and a pulsewidth of 53.8 μs, which was followed by an opposite polarity overshoot with a peak value of 8.5 kA. Our current records suggest the involvement of a long upward connecting positive leader in response to the approaching downward negative leader in the formation of this flash. Lightning location system (LLS) data indicate that a positive cloud-to-ground stroke occurred 1 ms prior to the first stroke of the flash. In this paper, we present a detailed description of the data associated with this event. Moreover, both a return stroke model and an M-component model are used to reproduce the far-field waveform of this bipolar stroke. The simulations result in a radiated electric field waveform that is similar to those of large bipolar events (LBEs) observed in winter thunderstorms in Japan. A sensitivity analysis of the used simulation models reveals that, by proper selection of the input parameters, all field waveform characteristics, except for the positive half-cycle width, can be made to fall in the range of LBE field characteristics reported in Japan.

Electromagnetic fields associated with the M-component mode of charge transfer
Article scientifique ArODES

Lixia He, Farhad Rachidi, Mohammad Azadifar, Marcos Rubinstein, Vladimir A. Rakov, Vernon Cooray, Davide Pavanello, Hongyan Xing

Journal of Geophysical Research: Atmospheres,  2019, vol. 124, no. 13, pp. 6791-6809

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Résumé:

In upward flashes, charge transfer to ground largely takes place during the initial continuous current (ICC) and its superimposed pulses (ICC pulses). ICC pulses can be associated with either M-component or leader/return‐stroke‐like modes of charge transfer to ground. In the latter case, the downward leader/return stroke process is believed to take place in a decayed branch or a newly created channel connected to the ICC‐carrying channel at relatively short distance from the tower top, resulting in the so‐called mixed mode of charge transfer to ground. In this paper, we study the electromagnetic fields associated with the M‐component charge transfer mode using simultaneous records of electric fields and currents associated with upward flashes initiated from the Säntis Tower. The effect of the mountainous terrain on the propagation of electromagnetic fields associated with theM‐component charge transfer mode (including classical M‐component pulses and M‐component‐type pulses superimposed on the initial continuous current) is analyzed and compared with its effect on the fields associated with the return stroke (occurring after the extinction of the ICC) and mixed charge transfer modes. For the analysis, we use a 2‐Dimentional Finite‐Difference Time Domain method, in which the M‐component is modeled by the superposition of a downward current wave and an upward current wave resulting from the reflection at the bottom of the lightning channel (Rakov et al., 1995, https://doi.org/10.1029/95JD01924 model) and the return stroke and mixed mode are modeled adopting the MTLE (Modified Transmission Line with Exponential Current Decay with Height) model. The finite ground conductivity and the mountainous propagation terrain between the Säntis Tower and the field sensor located 15 km away at Herisau are taken into account. The effects of the mountainous path on the electromagnetic fields are examined for classical M‐component and M‐component‐type ICC pulses. Use is made of the propagation factors defined as the ratio of the electric or magnetic field peak evaluated along the mountainous terrain to the field peak evaluated for a flat terrain. The velocity of theM‐component pulse is found to have a significant effect on the risetime of the electromagnetic fields. A faster traveling wave speed results in larger peaks for the magnetic field. However, the peak of the electric field appears to be insensitive to the M‐component wave speed. This can be explained by the fact that at 15 km, the electric field is still dominated by the static component, which mainly depends on the overall transferred charge. The contribution of the radiation component to the M‐component fields at 100 km accounts for about 77% of the peak electric field and 81% of the peak magnetic field, considerably lower compared to the contribution of the radiation component to the return stroke fields at the same distance. The simulation results show that neither the electric nor the magnetic field propagation factors are very sensitive to the risetimes of the current pulses. However, the results indicate a high variability of the propagation factors as a function of the branch‐to‐channel junction point height. For junction point heights of about 1 km, the propagation factors reach a value of about 1.6 for the E‐field and 1.9 for the H‐field. For a junction height greater than 6 km, the E‐field factor becomes slightly lower than 1. The obtained results are consistent with the findings of Li, Azadifar, Rachidi, Rubinstein, Paolone, et al. (2016, https://doi.org/10.1109/TEMC.2015.2483018) in which an electric field propagation factor of 1.8 was inferred for return strokes and mixed‐mode pulses, considering that junction points lower than 1 km or so would result in a mixed mode of charge transfer, in which a downward leader/return‐stroke‐like process is believed to take place. It is also found that the field enhancement (propagation factor) for return stroke mode is higher for larger ground conductivities. Furthermore, the enhancement effect tends to decrease with increasing current risetime, except for very short risetimes (less than 2.5 μs or so) for which the tendency reverses. Finally, model‐predicted fields associated with different charge transfer modes, namely, return stroke, mixed‐mode, classical M‐component, and M‐component‐type ICC pulse are compared with experimental observations at the Säntis Tower. It is found that the vertical electric field waveforms computed considering the mountainous terrain are in very good agreement with the observed data. The adopted parameters of the models that provide the best match with the measured field waveforms were consistent with observations. The values for the current decay height constant adopted in the return stroke and mixed‐mode models (1.0 km for the return stroke and 0.8 km for the mixed‐mode pulse) are lower than the value of 2.0 km typically used in the literature.

Analysis of a bipolar upward lightning flash based on simultaneous records of currents and 380-km distant electric fields
Article scientifique ArODES

Amirhossein Mostajabi, Farhad Rachidi, Dongshuai Li, Mohammad Azadifar, Marcos Rubinstein, Gerard Diendorfer, Wolfgang Schulz, Hannes Pichler, Vladimir A. Rakov, Davide Pavanello

Electric Power Systems Research,  2019, vol. 174, article no 105845

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Résumé:

In this paper, we present and discuss simultaneous records of current and wideband electric field waveforms at 380 km distance from the strike point associated with an upward bipolar flash initiated from the Säntis Tower. The flash contains 23 negative strokes and one positive stroke. The intervals between the groundwave and skywave arrival times are used to estimate ionospheric reflection heights for the negative return strokes using the so-called zero-to-zero and peak-to-peak methods. A full-wave, finite-difference time-domain (FDTD) analysis of the electric field propagation including the effect of the ionospheric reflections is also presented. FDTD simulation results are compared with the measured radiated electric field associated with the studied flash to evaluate the reference reflection height of the conductivity profile. It is also found that the ratio of the peak field to the current peak is about two times smaller for the positive pulse compared to negative pulses. This difference in the amplitudes can be attributed to a lower return stroke speed for the positive stroke compared to that for negative strokes, and also to the fact that the enhancement of the electric field due to the presence of the tower and the mountain might be more significant for negative pulses, which are characterized by faster risetimes compared to the positive one.

2018

An analysis of current and electric field pulses associated with upward negative lightning flashes initiated from the Säntis tower
Article scientifique ArODES

Lixia He, Mohammad Azadifar, Farhad Rachidi, Marcos Rubinstein, Vladimir A. Rakov, Vernon Cooray, Davide Pavanello, Hongyan Xing

Journal of Geophysical Research: Atmospheres,  2018, 123, 8, pp. 4045-4059

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Résumé:

We present a study on the characteristics of current and electric field pulses associated with upward lightning flashes initiated from the instrumented Säntis Tower in Switzerland. The electric field was measured 15 km from the tower. Upward flashes always begin with the initial stage composed of the upward‐leader phase and the initial‐continuous‐current (ICC) phase. Four types of current pulses are identified and analyzed in the paper: (1) return‐stroke pulses, which occur after the extinction of the ICC and are preceded by essentially no‐current time intervals; (2) mixed‐mode ICC pulses, defined as fast pulses superimposed on the ICC, which have characteristics very similar to those of return strokes and are believed to be associated with the reactivation of a decayed branch or the connection of a newly created channel to the ICC‐carrying channel at relatively small junction heights; (3) “classical” M‐component pulses superimposed on the continuing current following some return strokes; and (4) M‐component‐type ICC pulses, presumably associated with the reactivation of a decayed branch or the connection of a newly created channel to the ICC‐carrying channel at relatively large junction heights. We consider a data set consisting of 9 return‐stroke pulses, 70 mixed‐mode ICC pulses, 11 classical M‐component pulses, and 19 M‐component‐type ICC pulses (a total of 109 pulses). The salient characteristics of the current and field waveforms are analyzed. A new criterion is proposed to distinguish between mixed‐mode and M‐component‐type pulses, which is based on the current waveform features. The characteristics of M‐component‐type pulses during the initial stage are found to be similar to those of classical M‐component pulses occurring during the continuing current after some return strokes. It is also found that about 41% of mixed‐mode ICC pulses were preceded by microsecond‐scale pulses occurring in electric field records some hundreds of microseconds prior to the onset of the current, very similar to microsecond‐scale electric field pulses observed for M‐component‐type ICC pulses and which can be attributed to the junction of an in‐cloud leader channel to the current‐carrying channel to ground. Classical M‐component pulses and M‐component‐type ICC pulses tend to have larger risetimes ranging from 6.3 to 430 μs. On the other hand, return‐stroke pulses and mixed‐mode ICC pulses have current risetimes ranging from 0.5 to 28 μs. Finally, our data suggest that the 8‐μs criterion for the current risetime proposed by Flache et al. is a reasonable tool to distinguish between return strokes and classical M‐components. However, mixed‐mode ICC pulses superimposed on the ICC can sometimes have considerably longer risetimes, up to about 28 μs, as observed in this study.

2017

Analysis of lightning-ionosphere interaction using simultaneous records of source current and 380 km distant electric field
Article scientifique ArODES

Mohammad Azadifar, Dongshuai Li, Farhad Rachidi, Marcos Rubinstein, Gerhard Diendorfer, Wolfgang Schulz, Hannes Pichler, Vladimir A. Rakov, Mario Paolone, Davide Pavanello

Journal of Atmospheric and Solar-Terrestrial Physics,  2017, vol. 159, pp. 48-56

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Résumé:

We present simultaneous current and wideband electric field waveforms at 380 km associated with upward lightning flashes initiated from the Säntis Tower, Switzerland. To the best of our knowledge, the dataset presented in this study includes the first simultaneous records of lightning currents and associated fields featuring ionospheric reflections for natural upward flashes, and the longest distance at which natural upward lightning fields have been measured simultaneously with their causative currents. The intervals between the groundwave and skywave arrival times are used to estimate ionospheric reflection heights during day and night times using the so-called zero-to-zero and peak-to-peak methods. During daytime, the mean ionospheric reflection heights, obtained using the two different delay estimation approaches, are about 78 and 76 km, corresponding to the D layer. The mean reflection height at nighttime is about 90 and 89 km, corresponding to the E layer. We present a full-wave, finite-difference time-domain (FDTD) analysis of the electric field propagation including the effect of the ionospheric reflections. The FDTD simulation results are compared with the measured fields associated with upward flashes initiated from the Säntis Tower. It is found that the model reproduces reasonably well the measured waveforms and the times of arrival of the one-hop and two-hop skywaves relative to the groundwave.

2016

Bipolar lightning flashes observed at the Säntis tower :
Article scientifique ArODES
do we need to modify the traditional classification ?

Mohammad Azadifar, Farhad Rachidi, Marcos Rubinstein, Vladimir A. Rakov, Mario Paolone, Davide Pavanello

Journal of Geophysical Research: Atmospheres,  2016, vol. 121, no. 14, pp. 14,117-14,126

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Résumé:

We present and discuss current waveforms associated with 13 bipolar lightning flashes recorded at the Säntis Tower during the period from June 2010 to January 2015. During this period, a total of 427 flashes were recorded, of which 13 (3%) were classified as bipolar flashes. The majority of the recorded flashes (10 out of 13) exhibited a polarity reversal during the initial continuous current, therefore belonging to Category I according to the classification proposed by Rakov (2003). Of the three remaining flashes, two were characterized by different polarities of the initial stage current and the following return stroke or strokes (Category II), and one flash involved return strokes of opposite polarity within the same flash (Category III). In Category I bipolar flashes, the polarity reversal is usually assumed to be associated with in-cloud processes. However, two of our 10 Category I flashes appeared to be each a sequence of two upward discharges of opposite polarity, initiated from the tower within tens of milliseconds of each other. This is the first time that such a sequence has been observed from the same tower. We suggest that the traditional classification of bipolar flashes should be modified to distinguish between two types of Category I flashes: those in which the polarity reversal during the initial stage is associated with in-cloud processes (Category Ia) and those in which the polarity reversal is due to initiation of two opposite-polarity leaders from the tower (Category Ib).

Fast initial continuous current pulses versus return stroke pulses in tower-initiated lightning
Article scientifique ArODES

Mohammad Azadifar, Farhad Rachidi, Marcos Rubinstein, Vladimir A. Rakov, Mario Paolone, Davide Pavanello, Stefan Metz

Journal of Geophysical Research: Atmospheres,  2016, vol. 121, pp. 6425–6434

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Résumé:

We present a study focused on pulses superimposed on the initial continuous current of upward negative discharges. The study is based on experimental data consisting of correlated lightning current waveforms recorded at the instrumented Säntis Tower in Switzerland and electric fields recorded at a distance of 14.7 km from the tower. Two different types of pulses superimposed on the initial continuous current were identified: (1) M-component-type pulses, for which the microsecond-scale electric field pulse occurs significantly earlier than the onset of the current pulse, and (2) fast pulses, for which the onset of the field matches that of the current pulse. We analyze the currents and fields associated with these fast pulses (return-stroke type (RS-type) initial continuous current (ICC) pulses) and compare their characteristics with those of return strokes. A total of nine flashes containing 44 RS-type ICC pulses and 24 return strokes were analyzed. The median current peaks associated with RS-type ICC pulses and return strokes are, respectively, 3.4 kA and 8 kA. The associated median E-field peaks normalized to 100 km are 1.5 V/m and 4.4 V/m, respectively. On the other hand, the electric field peaks versus current peaks for the two data sets (RS-type ICC pulses and return strokes) are characterized by very similar linear regression slopes, namely, 3.67 V/(m kA) for the ICC pulses and 3.77 V/(m kA) for the return strokes. Assuming the field-current relation based on the transmission line model, we estimated the apparent speed of both the RS-type ICC pulses and return strokes to be about 1.4 × 108 m/s. A strong linear correlation is observed between the E-field risetime and the current risetime for the ICC pulses, similar to the relation observed between the E-field risetime and current risetime for return strokes. The similarity of the RS-type ICC pulses with return strokes suggests that these pulses are associated with the mixed mode of charge transfer to ground.

On lightning electromagnetic field propagation along an irregular terrain
Article scientifique ArODES

Dongshuai Li, Mohammad Azadifar, Farhad Rachidi, Marcos Rubinstein, Mario Paolone, Davide Pavanello, Stefan Metz, Qilin Zhang, Zhenhui Wang

IEEE Transactions on Electromagnetic Compatibility,  2016, vol. 58, no. 1, pp

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Résumé:

In this paper, we present a theoretical analysis of the propagation effects of lightning electromagnetic fields over a mountainous terrain. The analysis is supported by experimental observations consisting of simultaneous records of lightning currents and electric fields associated with upward negative lightning flashes to the instrumented Säntis tower in Switzerland. The propagation of lightning electromagnetic fields along the mountainous region around the Säntis tower is simulated using a full-wave approach based on the finite-difference time-domain method and using the two-dimensional topographic map along the direct path between the tower and the field measurement station located at about 15 km from the tower. We show that, considering the real irregular terrain between the Säntis tower and the field measurement station, both the waveshape and amplitude of the simulated electric fields associated with return strokes and fast initial continuous current pulses are in excellent agreement with the measured waveforms. On the other hand, the assumption of a flat ground results in a significant underestimation of the peak electric field. Finally, we discuss the sensitivity of the obtained results to the assumed values for the return stroke speed and the ground conductivity, the adopted return stroke model, as well as the presence of the building on which the sensors were located.

2015

Evaluation of the performance characteristics of the european lightning detection network EUCLID in the alps region for upward negative flashes using direct measurements at the instrumented Säntis tower
Article scientifique ArODES

Mohammad Azadifar, Farhad Rachidi, Marcos Rubinstein, Mario Paolone, Gerhard Diendorfer, Hannes Pichler, Wolfgang Schulz, Davide Pavanello, Carlos Romero

Journal of Geophysical Research: Atmospheres,  2015, vol. 121, no. 2, pp. 595-606

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Résumé:

In this paper, we present a performance analysis of the European Cooperation for Lightning Detection (EUCLID) lightning detection network using data obtained on lightning currents measured at the Säntis Tower (located in northeastern of Switzerland) from June 2010 to December 2013. In the considered period of analysis, a total number of 269 upward negative flashes were recorded at the Säntis Tower. The performance of the EUCLID lightning detection network is evaluated in terms of detection efficiency, location accuracy, and peak current estimates for upward flashes. Excluding flashes containing only an initial continuous current with no superimposed pulses exceeding 2 kA, the flash detection efficiency for upward flashes is estimated to be 97%. The recorded flashes contained a total of 2795 pulses (including return strokes and International Conference on Communications pulses characterized by risetimes lower than 8 µs and peaks greater than 2 kA). The overall pulse detection efficiency was found to be 73%. For pulses with peak values higher than 5 kA, the pulse detection efficiency was found to be about 83%. Peak current estimates provided by the EUCLID network were found to be significantly larger than their directly measured counterparts. This overestimation might be attributed to the enhancement of the radiated electromagnetic fields associated with the presence of the tower and the mountain. The median of the absolute distance error, defined as the median distance between the Säntis Tower location and the EUCLID's stroke locations, was found to be 186 m, the majority of large location errors being associated with measured current peaks lower than 10 kA. The analysis revealed also that the location accuracy of the EUCLID network improved significantly in 2013 as a result of an upgrade in the location algorithms to take into account propagation effects.

2009

On the current peak estimates provided by lightning detection networks for lightning return strokes to tall towers
Article scientifique ArODES

Davide Pavanello, Fahrad Rachidi, Wasyl Janischewskyj, Marcos Rubinstein, Volodymyr O. Shostak, Carlo Alberto Nucci, Kenneth L. Cummins, Ali M. Hussein, Jen-Shih Chang

IEEE Transactions on electromagnetic compatibility,  2009, vol. 51, no 3, pp. 453 - 458

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Résumé:

The peak current estimation of lightning detection networks for strikes to tall towers is discussed in this paper. Such systems are sometimes calibrated using return-stroke current data obtained by means of rocket-triggered lightning or instrumented towers of relatively short height. However, for strikes to electrically tall towers, they tend to overestimate the return-stroke current peak. In this case, in fact, the associated radiated electromagnetic fields, from which the return-stroke current is estimated, experience a significant enhancement with respect to the field that would be radiated if the same return stroke was initiated at ground level or on a short tower. Two approaches to correct the current estimates of a lightning detection network for a lightning strike to a tall tower are discussed and applied to the current measurements obtained at the CN Tower in Toronto in the summer of 2005, for which estimates were available from the North American Lightning Detection Network (NALDN). It is shown that correcting the NALDN estimates using the so-called tower factor obtained from theoretical studies results in an excellent estimation of lightning current peaks.

2005

Far-field-current relationship based on the TL model for lightning return strokes to elevated strike objects
Article scientifique ArODES

José Luis Bermudez, Farhad Rachidi, Marcos Rubinstein, Wasyl Janischewskyj, Volodymyr O. Shostak, Davide Pavanello, Jen Shih Chang, Ali M. Hussein, Carlo Alberto Nucci, Mario Paolone

IEEE Transactions on electromagnetic compatibility,  2005, vol. 47, no. 1, pp. 146 - 159

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Résumé:

New general expressions relating lightning return stroke currents and far radiated electric and magnetic fields are proposed, taking into account the effect of an elevated strike object, whose presence is included as an extension to the transmission line (TL) model. Specific equations are derived for the case of tall and electrically short objects. The derived expressions show that, for tall structures (when the round-trip propagation time from top to bottom within the tower is greater than the current zero-to-peak risetime), the far field is enhanced through a factor with respect to an ideal return stroke initiated at ground level. The enhancement factor can be expressed in terms of the return stroke wavefront speed v, the speed of light in vacuum c, and the current reflection coefficient at the top of the elevated strike object. For typically negative values of this top reflection coefficient, lightning strikes to tall towers result in a significant enhancement of the far electromagnetic field. Expressions relating the far electromagnetic field and the return stroke current are also presented for electrically short towers and for very long return stroke current wavefronts. For the case of return strokes initiated at ground level (h=0), these expressions represent a generalization of the classical TL model, in which the reflections at the ground are now taken into account. We describe also simultaneous measurements of return stroke current and its associated electric and magnetic fields at two distances related with lightning strikes to the 553-m-high Toronto Canadian National (CN) Tower performed during 2000 and 2001. The derived expressions for tall strike objects are tested versus obtained sets of simultaneously measured currents and fields associated with lightning strikes to the CN Tower, and a reasonable agreement is found. Additionally, it is shown that the peak of the electromagnetic field radiated by a lightning strike to a 553-m-high structure is relatively insensitive to the value of the return stroke velocity, in contrast to the lightning strikes to ground.

2021

Säntis lightning research facility instrumentation
Conférence ArODES

Antonio Sunjerga, Amirhossein Mostajabi, Mario Paolone, Farhad Rachidi, Mohammad Azadifar, Abraham Rubinstein, Marcos Rubinstein, Carlos Romero, Davide Pavanello, Pasan Hettiarachchi, Vernon Cooray, David Smith

Proceedings of the 35th International Conference on Lightning Protection (ICLP), XVI International Symposium on Lightning Protection (SIPDA)

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Résumé:

The Säntis Tower was instrumented in May 2010 to measure currents of lightning discharges striking the tower. Since then the system has been recurrently updated and expanded. Currently, data associated with lightning strikes to the tower are collected at five different sites. The facility is equipped with a current measurement system, three electric field antennas, an electrostatic field mill, two x-rays sensors, a high-speed camera and four full HD cameras. This paper presents the latest measurement configuration at the facility.

2019

Two possible scenarios for the formation of category 1 bipolar lightning flashes
Conférence ArODES

Mohammad Azadifar, Quanxin Li, Marcos Rubinstein, Farhad Rachidi, Vladimir Rakov, Davide Pavanello

Proceedings of the 2019 11th Asia-Pacific International Conference on Lightning (APL), 12-14 June 2019, Hong-Kong, Hong-Kong

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Résumé:

We present and discuss the current and electric field waveforms associated with two upward bipolar lightning flashes that occurred at the Säntis Tower. According to the traditional classification of bipolar flashes, both observed flashes could be classified as Category 1 flashes. The first one belongs to the subcategory la in which the polarity reversal during the initial stage is associated with an in-cloud process, while the second one involves the sequential initiation of two opposite-polarity leaders from the tower.

2018

On the similarity of electric field signatures of upward and downward negative leaders
Conférence ArODES

Mohammad Azadifar, Marcos Rubinstein, Farhad Rachidi, Vladimir A. Rakov, Davide Pavanello, Stefan Metz

Proceedings of the 34th International Conference on Lightning Protection (ICLP)

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Résumé:

We report on general characteristics of simultaneous channel-base current and distant electric fields for five upward positive flashes recorded at the Säntis tower in Summer 2014. We describe the salient features of the upward negative leader process initiating upward positive flashes and compare them with those of the downward negative leader process found in the literature. Our observations show considerable similarity between those two processes.

Modeling of different charge transfer modes in upward flashes constrained by simultaneously measured currents and fields
Conférence ArODES

Lixia He, Mohammad Azadifar, Quanxin Li, Marcos Rubinstein, Vladimir A. Rakov, Arturo Mediano, Davide Pavanello, Mario Paolone, Hongyan Xing, Farhad Rachidi

Proceedings of 2018 IEEE International Symposium on Electromagnetic Compatibility and 2018 IEEE Asia-Pacific Symposium on Electromagnetic Compatibility (EMC/APEMC), 14-18 May 2018, Singapore, Singapore

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Résumé:

The purpose of the paper is to investigate charge transfer modes in upward lightning flashes by means of numerical simulation constrained by concurrent observations of electromagnetic fields and currents. In particular, we focus on different types of pulses occurring in upward negative flashes. The MTLE return stroke model is used to compute the electric fields associated with return strokes and mixed-mode pulses, while the M-component model of Rakov et al. (1995) is used to compute electric fields associated with M-components and Mcomponent-type ICC pulses. The simulation results are constrained by experimental data consisting of simultaneous records of lightning currents and electric fields associated with upward flashes at the Säntis tower. The inferred velocities for Mcomponent and M-component-type ICC pulses range from 2.0x107 m/s to 9.0x107 m/s, and the corresponding junction point heights range from 1.0 km to 2.0 km. The inferred pulse velocities for return strokes and mixed-mode pulses range from 1.3x108 m/s to 1.65x108 m/s. The inferred current attenuation constants of the MTLE model obtained in this study range from 0.3 km to 0.8 km, lower than the value of 2.0 km suggested in previous studies. The obtained results confirm the similarity of mixed-mode charge transfer to ground with return strokes on the one hand, and of the M-component-type ICC with classical M-components mode of charge transfer on the other hand.

2017

Mixed integer programming model for the operation of an experimental low-voltage network
Conférence ArODES

Stefano Lilla, Alberto Borghetti, Fabio Napolitano, Fabio Tossani, Davide Pavanello, Dominique Gabioud, Yann Maret, Carlo Alberto Nucci

Proceedings of 2017 IEEE Manchester PowerTech, 18-22 June 2017, Manchester, UK

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Résumé:

The paper deals with the modeling and analysis of low voltage (LV) power distribution networks feeding residential, commercial and small industrial consumers including distributed generation units and storage systems. It focuses on an optimization model for the energy management system of the experimental microgrid built at the University of Applied Sciences and Arts of Western Switzerland, HES-SO Valais-Wallis, Sion. For this purpose, a mixed integer linear programming (MILP) model is presented, which takes into account the unbalanced operation of the LV network and the presence of the neutral wire. The validation of the accuracy of the model through the mentioned experimental microgrid and an analysis of some simulation results for a 24 hours horizon are presented too.

2016

An update on the measurements of lightning currents and electromagnetic fields associated with flashes to the Säntis tower in Switzerland
Conférence ArODES

Mohammad Azadifar, D. Li, Mario Paolone, Davide Pavanello, Farhad Rachidi, Marcos Rubinstein

Proceedings of International Colloquium on Lightning and Power Systems, 27-29 June 2016, Bologna, Italy

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Résumé:

The Säntis tower was instrumented in May 2010 [1] and more than 500 flashes were successfully recorded during its first five years of operation,. Preliminary statistical results during the first two years of operation were gathered and presented in [2] and [3]. In this paper, we present an update on the obtained data during 2014 and 2015. We also present results of simultaneously recorded currents and electric fields measured about 14.7 km away from the tower.

Simultaneous current and distant electric field waveforms from upward lightning :
Conférence ArODES
effect of ionospheric reflection

Mohammad Azadifar, Dongshuai Li, Farhad Rachidi, Marcos Rubinstein, Gerhard Diendorfer, Hannes Pichler, Mario Paolone, Davide Pavanello

Proceedings of 24th International Lightning Detection Conference (ILDC)

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Résumé:

We present simultaneous current and wideband electric field waveforms at 380 km associated with upward flashes initiated from the Säntis Tower. To the best of the authors’ knowledge, the presented dataset in this study includes the first simultaneous records of lightning currents and associated fields featuring ionospheric reflections, and the longest distance at which lightning fields have been measured simultaneously with the current. Electric field data are used to evaluate ionospheric reflection characteristics during day and night times using the so- called zero-zero and peak-peak methods. During daytime, the estimates for the ionospheric reflection height is about 80 km, corresponding to the D layer. The estimated height at night time is about 90 km, corresponding to the E layer. Finally, we present a full-wave, finite-difference time-domain (FDTD) analysis of the field propagation including the effect of the ionospheric reflection and compare the results with experimental data.

2015

Characteristics of electric fields of upward negative stepped leaders
Conférence ArODES

Mohammad Azadifar, Farhad Rachidi, Marcos Rubinstein, Mario Paolone, Vladimir A. Rakov, Davide Pavanello, Stefan Metz, Carlos Romero

Proceedings of the 2015 International Symposium on Lightning Protection (XIII SIPDA)

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Résumé:

We report simultaneous measurements of vertical electric fields and currents associated with positive flashes to the Säntis tower. The fields were measured at a distance of 14.7 km from the tower. All the data correspond to type-2 positive flashes characterized by currents with relatively slow rising portion on which oscillatory pulse trains, inferred to be due to an upward negative stepped leader, are superimposed. Bipolar electric field and current pulses associated with the upward negative stepped leader are examined and analyzed. The widths of the initial and second half cycles are found to be similar. The peak of the initial half cycle is found to be, on average, about twice as high as the peak of the second half cycle. A nearly linear correlation is found between the field peaks and associated current peaks.

Protection and automation test bench associated to a reduced-scale model of a power system for teaching purposes
Conférence ArODES

Thomas Ritler, Davide Pavanello, Dominique Gabioud

Proceedings of PAC World, 29 June-2 July 2015, Glasgow, Scotland

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2014

An update on the charaterictics of positive flashes recorded on the Säntis Tower
Conférence ArODES

Mohammad Azadifar, Mario Paolone, Davide Pavanello, Farhad Rachidi, Vladimir A. Rakov, Carlos Romero, Marcos Rubinstein

Proceedings of 2014 International Conference on Lightning Protection (ICLP), 11-18 October 2014, Shanghai, China

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Résumé:

We present an update on the characteristics of positive flashes recorded on the Säntis Tower in Switzerland from May 2010 to January 2013, during which period 38 positive flashes were recorded. Out of the 38 recorded flashes, 1 was identified as a normal downward flash, 5 were classified as type-1 flashes (characterized by a large unipolar impulse) and the rest of the flashes (32) were classified as type-2 flashes (characterized by a slow waveform with superimposed pulse train). We present a summary of the characteristics of the lightning current parameters for type-1 and type-2 flashes separately and for both types combined. We also present a comparison between the present results corresponding to type-1 flashes and Berger et al.'s data for flashes with large impulsive currents. A similar comparison is presented between type-2 flashes in this study and Berger et al.'s data for flashes without large impulsive currents. In the latter comparison, the most significant differences between the two datasets are in the peak current and the amount of transferred charge, both of which are substantially larger in our type-2 flash dataset. We finally present a discussion of the oscillatory pulse trains in type-2 flashes. Our data are found to be, in general, consistent with those observed at the Gaisberg tower. However, the overall leader pulse duration and the individual pulse duration observed at Säntis are higher than their counterparts at Gaisberg.

2012

A statistical analysis on the risetime of lightning current pulses in negative upward flashes measured at Santis tower
Conférence ArODES

Carlos Romero, Mario Paolone, Farhad Rachidi, Marcos Rubinstein, Davide Pavanello, Dave V. Giri

Proceedings of 2012 International Conference on LIghtning Protection (ICLP), 2-7 September 2012, Vienna, Austria

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Résumé:

We present statistical data on the risetime of lightning current pulses in negative upward flashes measured on the Säntis tower in 2010 and 2011. Two different definitions were used to determine the current risetime. The first is the t 10-90 rise time usually adopted in lightning applications and lightning standards. The second one is the risetime associated with the maximum rate of rise t mr given by the ratio between the current peak and the current maximum derivative. The obtained statistical values for t mr are found to be substantially smaller than those for the classical t 10-90 , the median and geometrical mean for t 10-90 (0.9 μs and 1.08 μs, respectively) being 3 times larger than those associated with t mr (0.3 μs and 0.37 μs). The relation between the risetime and the maximum significant frequency of the measured pulses is also discussed. It is shown that, in general, the t mr definition is more consistent with the maximum frequency content of the signals, compared with the t 10-90 risetime.

Some characteristics of positive and bipolar lightning flashes recorded on the Santis tower in 2010 and 2011
Conférence ArODES

Carlos Romero, Marcos Rubinstein, Farhad Rachidi, Mario Paolone, Vladmir A. Rakov, Davide Pavanello

Proceedings of 2012 International Conference on Lightning Protection (ICLP), 2-7 September 2012, Vienna, Austria

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Résumé:

We present an analysis of measured current waveforms associated with positive and bipolar flashes recorded on the Säntis tower, Switzerland, from May 2010 till January 2012. The overall number of recorded flashes in the considered period was 201, of which 30 were of positive polarity (effectively transported positive charge to ground) and three were bipolar. The recorded positive flashes were mainly concentrated in the summer months, August being the month during which most of them occurred (6 events in 2010 and 16 events in 2011). The observed positive flashes are characterized by a median peak current of 11.8 kA, and a median flash duration of 80 ms. These values are consistent with those associated with the data recorded at the Gaisberg Tower in Austria. On the other hand, the amount of transferred charge is substantially larger in our dataset, with a median value of 169 C (6 times as large as the values obtained in Monte San Salvatore and in Japan, and 3 times as large as the value obtained in Austria). Eight flashes out of 30 transported positive charge to the ground in excess of 500 C. The obtained results confirm also the findings of Saba et al. according to which positive lightning flashes may combine high peak currents with high charge transfers (or flash durations). The three bipolar flashes recorded during the considered time period occurred during one storm occurred on August 27, 2011. The relative number of bipolar flashes (1.5%) is found to be lower than the values reported in previous studies in Austria and in Switzerland (3 to 6%). On the basis of the classification proposed by Rakov, two of the three observed bipolar flashes belonged to Type 2 and one to Type 3.

Analysis of lightning detection network data for selected areas in Canada
Conférence ArODES

Volodymyr Shostak, Olexandr Bormotov, Davide Pavanello, Wasyl Janischewskyj, Farhad Rachidi

Proceedings of 2012 International Conference on Lightning Protection (ICLP), 2-7 September 2012, Vienna, Austria

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Résumé:

An analysis of Canadian Lightning Detection Network (CLDN) data recorded during years 2004 - 2006 is performed for two selected areas in Canada within a 20-km radius around two tall structures: the CN Tower (CNT, 553 m) in Toronto and the Superstack (SS, 380 m) in Sudbury. The explored lightning characteristics include stroke polarity, lake water or land termination (WT or LT), ground stroke densities N gs , stroke peak currents (including values of I 50% , I 95% , I 5% ), distributions of parameters. The results show noticeable differences between characteristics of lightning terminated to lake water and land. In Toronto area (N gs ≈ 3.24 strokes/(km 2 ·year)), a commonly accepted feature, according to which positive strokes exhibit dominating peak currents in comparison to negative ones, is confirmed only for WT lightning (not close to the CNT), especially in the range of high currents. For LT lightning in the range of current amplitudes close to 50% values, the negative strokes are characterized by larger peaks (by more than 30%) with respect to positive ones. No positive strokes to water were recorded within 5 km near the CNT during the period of analysis. While WT events exhibit a lower N gs than LT ones, they show larger peak currents. The Sudbury area, characterized by a lower lightning activity (N gs ≈ 0.91 strokes/(km2·year)), shows the common relation between peak currents of positive and negative polarities (first are dominating). For the SS, the estimated number of upward lightning looks rather low: 0.47 strokes or 0.37 flashes per year. For the CNT, it is about 32 strokes or 14 upward flashes per year. Distributions of N gs along the distance from the tall objects, beside the increased levels near object, contain dips next to object (up to 3 - 7 km).

2006

On the effect of the finite ground conductivity on electromagnetic field radiated by lightning to tall towers
Conférence ArODES

Vernon Cooray, Gerhard Diendorfer, Carlo Alberto Nucci, Davide Pavanello, Farhad Rachidi, Marley Becerra, Marcos Rubinstein

Proceedings of the 28th International Conference on Lightning Protection ICLP, 18-22 September 2006 Kanazawa, Japan

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Résumé:

In this paper it is shown how the finitely conducting ground modifies the signature of the radiation field of return strokes striking tall towers. Results are presented for different tower heights and for different ground conductivities varying the current risetime in the return stroke model. The results show that the attenuation of the initial peak of the radiation field resulting from the propagation over finitely conducting ground depends strongly on the current risetime, the tower height and the ground conductivity. In general, the attenuation of the radiation field of lightning flashes striking tall towers is larger than that striking flat ground. In the case where the ground conductivity is extremely poor, namely 0.0001 S/m, the attenuation of the peak radiation field may reach as much as 70% in the case of lightning flashes striking a 300- m tall tower.

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